The present invention relates to a steering gear and particularly to a hydraulic power assist steering gear.
Hydraulic power assist steering gears are well known. Typically, such steering gears include a housing which defines a chamber. A piston divides the chamber into first and second chamber portions. The piston is movable in a work stroke within the chamber due to fluid pressure. A steering valve directs fluid into one of the chamber portions and vents the other chamber portion to effect movement of the piston in a given direction. An input shaft is rotated by the driver of the vehicle to effect actuation of the steering valve. The piston is drivingly connected to the vehicle steering mechanism to effect actuation thereof upon movement of the piston.
The vehicle steering mechanism has stops which limit the amount of movement of the steered wheels in both directions of turning. Typically, a stop is fixed to the axle and another stop is movable with the steered wheel and can engage the stop fixed to the axle to limit movement of the steered wheels in one direction. Similar stops engage to limit movement of the steered wheels in the opposite direction. The amount of movement of the steered wheels before the stops engage may vary from vehicle to vehicle because of manufacturing tolerances and other factors. The piston in the power steering gear moves through a work stroke, the length of which is proportioned to the amount of movement of the steered wheels before the stops engage.
A known steering gear includes relief valves which are carried by the piston. The relief valves, commonly known as end-of-stroke relief valves, allow fluid communication between the chamber portions on opposite sides of the piston as the piston approaches the end of its work stroke in either direction and just prior to engagement of the stops. The end of stroke relief valves operate to preclude the trapping of hydraulic fluid in the fluid exhausting chamber portion, and prevent high pressure build-up which could damage the steering gear housing. The relief valves as shown in U.S. Pat. No. 3,935,790 include a valve seat fixed to the piston and a valve member which moves relative to its valve seat. As the piston approaches the end of its work stroke, one relief valve at the high pressure chamber portion is open and the valve member of the other relief valve moves relative to its valve seat to open the valve. This allows fluid communication between the chamber portions on opposite sides of the piston.
Typically, the relief valve member moves relative to its valve seat upon engagement with an adjustment screw located in the housing of the steering gear. Upon initial engagement with the adjustment screw and continued movement of the piston after such engagement, the valve member moves relative to its valve seat to effect opening of the relief valve to communicate the opposite chamber portions. The relief valves function to communicate the chamber portions when the steering mechanism stops are engaged. This relieves the pressure on the power steering pump and reduces the forces acting on the mechanical parts of the steering mechanism.
The location of the piston where a relief valve opens is critical since the relief valve is to open just prior to engagement of the steering mechanism stops. This location can be adjusted by turning the adjustment screw, which then engages the valve member at a different piston location.
The adjustment of the adjusting screws has been accomplished in the past by two persons. One person rotates the steering wheel until the steering mechanism stops are engaged. When the stops are engaged the adjustment screw is adjusted by another person to move the valve member to its open position. Obviously, this is a cumbersome and costly procedure.